This section provides background information related to the present disclosure which is not necessarily prior art.
The automobile industry is actively working to develop alternative powertrains in an effort to significantly reduce or eliminate the emissions exhausted into the air by conventional powertrains equipped with an internal combustion engine. Significant development has been directed toward electric vehicles (EV) that are equipped with one or more electric traction motors. For example, some electric vehicles are only powered by the electric motor(s) and rely solely on the electrical energy stored in an on-board battery pack. However, some other electric vehicles, commonly referred to as hybrid electric vehicles (HEV), have both an internal combustion engine and one or more traction motors.
There are two types of hybrid electric vehicles, namely, series hybrid and parallel hybrid. In series hybrid electric vehicles, tractive power is generated and delivered to the wheels by the electric traction motor(s) while the internal combustion engine is used to drive a generator for charging the battery pack. In parallel hybrid electric vehicles, the traction motor(s) and the internal combustion engine work independently or in combination to generate and deliver tractive power to the wheels.
Various types of electric and hybrid powertrain arrangements are currently being developed. For example, some electric vehicles are equipped with wheel-mounted electric traction motor/gearbox assemblies. In such an arrangement, a fixed-ratio gear reduction is provided between the traction motor and the driven wheel hub. In other arrangements, an electric drive module (EDM) is used to generate and deliver tractive power to a pair of wheels. The electric drive module may include an electric traction motor, a final drive assembly including a differential unit that is adapted for connection to the wheels, and a reduction gearset directly coupling an output component of the traction motor to an input component of the differential unit. The reduction gearset may be based on a layshaft configuration or a planetary configuration for the purpose of providing a desired speed reduction and torque multiplication between the traction motor and the differential unit. Thus, the electric drive module is essentially a single-speed or “direct drive” transaxle that can be adapted to drive either the front wheels or the rear wheels of the vehicle.
In some other electric or hybrid vehicles, the electric drive module can include a pair of electric traction motors each mounted in-board of the wheel and having a gear reduction unit coupled to drive an axleshaft for transmitting tractive power to the wheel. These traction motors can be independently controlled to distribute balanced power and traction to each wheel without concern for inter-wheel slip associated with conventional EDM's equipped with a differential unit. In a vehicle equipped with such a “dual motor” electric drive module, this balancing of power and traction can provide side-to-side (i.e., “left-to-right”) control in either of a front wheel drive (FWD) or rear wheel drive (RWD) vehicular configuration. Alternatively, electric drive modules can be used at both the front and rear of the vehicle to provide four independently controllable traction motors and generate balanced power and traction for both left-to-right and front-to-rear control to establish a four-wheel drive (4WD) vehicular configuration. Such dual motor electric drive modules typically include fixed-ratio gearsets between the traction motor and the axleshaft. Fixed-ratio gearsets may, however, require a compromise between low end torque and top end speed as well as the need to utilize larger motors to accommodate all torque and speed requirements.
In view of the above, it would be beneficial to provide technology that addresses and overcomes these issues so as to facilitate the design and manufacture of electric drive vehicles that are in electric vehicles having optimized power and traction delivery characteristics.